The problem seems to be that when creating new rows dynamically, you are setting the value of the input field to an empty string. That's why the new line doesn't show the current date.
You can modify the BtnAdd() function to set the value of the new input field to the current date. You can get the current date in JavaScript like this:
new Date().toISOString().split('T')[0]
.
Take a look:
function BtnAdd() {
/*Add Button*/
var v = $("#TRow").clone().appendTo("#TBody") ;
var currentDate = new Date().toISOString().split('T')[0]; // Get the current date
$(v).find("input").val(currentDate); // Set the value of the new input field to the current date
$(v).find("input").autocomplete({ source: 'backend-script.php' });
$(v).removeClass("d-none");
$(v).find("th").first().html($('#TBody tr').length - 1);
}